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GI Secretion :male-scientist: (Digestion (Fats (Minor (Cholesterol,…
GI Secretion :male-scientist:
Main hormonal regulation
Gastrin
Increases gastric motility and secretion
Cholecystokinin (Small Intestine)
Stimulates pancreatic enzyme secretion
Gall bladder contraction
Reduces gastric motility
Secretion (Small intestine)
Increases pancreatic and intestinal bicarbonate secretion
Salivary secretion
Types
Serous
alpha-amylase
digestion of starch and carbohydrate
Mucous
Mucin
Aid movement through esophagus
Surface protection of esophagus
Location
Parotid
Only serous
Digestion
Submaximal
Both serous and mucous
Sublingual
Only mucous
Gastric secretion
Mucous cells
Mucous
Chief cells
Pepsinogen
Parietal cells
HCl
G cells
Gastrin
Induces the secretion of pepsinogen and HCl from respective cells
Increases gastric and ileal motility
Relaxes ileal sphincter
Induces mass movement in GIT
To prepare stomach for new meal entry
Stimulated when food enters stomach
Stimulated from anthrum
Anthral distention triggers gastrin production
increase gastrin secretion
:coffee:
:wine_glass:
digested protein
HCl secretion mechanism
140mmol/L
Isotonic to blood plasma
4 million times higher than in blood
Metabolism produces CO2
CARBONIC ANHYDRASE enzyme
Combines CO2 and H20 to form H2CO3
H2CO3 breaks down to
H+ enters stomach lumen
HCO3 enters bloodstream
Cl is taken up by active transport
Combines with H+ to form HCl
Blockade of carbonic anhydrase
No HCl
Neural Regulation of Gastric regulation
Cephalic phase
Accounts for 10% of gastric secretion
Involves sight, smell and thought
Parasympathetic reflexes (Vagal)
Control gastric secretion and motility
Gastric phase
Accounts for 2/3 of all gastric secretion
When food enters stomach
Vagal stimulation + local innervation
Increases secretion
Gastrin activated
Intestinal phase
Presence of food in intestine decreases gastric secretion and motility
Vagal and local reflexes
Decreases parasympathetic signals
Effect of cholecystokinin and secretin
Digestion
Hydrolysis: returning water to
Fat/Triglycerides
Glycerol
3 fatty acids
Polysaccharides
Disaccharides
Monosaccharides
Protein
Amino acids
Carbohydrates
Starch
Digested to maltose and isomaltose before entering ileum
Epithelial cells
Have enzymes on their brush borders
Isomaltase
Maltase
Sucrase
Lactase
Resulting monosaccharides are immediately absorbed in the lower jejunum and upper ileum
Fats
Most common: neutral fat
Triglycerides
Minor
Cholesterol
Cholesterol esters
Phospholipids
Main digestion via pancreatic lipase (95-99%)
Little by gastric lipase
Brush border
Enteric lipase
Resulting products absorbed in the jejunum
Proteins
Stomach
Pepsin
Active between pH 2-5
Begins digestion of all proteins, including collagen
Peptones and large polypeptides
Intestine
Pancreatic enzymes
Trypsin
Chymotrypsin
Carboxypeptidase
Converts to dipeptides or amino acids
Brush border enzymes
Aminopeptidase
Dipeptidase
Resulting amino acids absorbed in upper ileum/lower jejunum
Large Intestine
Little digestion
Large bacteria population digests small amount of fibre
Produces
Vitamin B12
Absorbed in terminal ileum
Vitamin K
Absorbed in large intestine
Riboflavin
Thiamine
Biotin
Absorbs
Na/K/Cl, water
Small intestine
Duodenum
Absorbs most minerals (except Na, K, Cl)
Upper ileum, lower jejunum
monosaccharides, amino acids, water soluble vitamin
Jejunum
Lipids, fat-soluble vitamins
Terminal ileum
vitamin B12